1. Field of Invention
The present disclosure is generally related to a tool for lamination of a metal foil and a polymer film at high temperatures, and methods of manufacturing and using the tool.
2. Description of the Related Art
Thin thermoplastic polyimide film and metal foil structural composite heaters have widespread use in aerospace applications, such as with/in propellers, helicopter rotors, nose cones, spinners, stators, gas turbine inlet ducts, nacelles and wings. For operation above 300° F., the heater assemblies are processed at temperatures greater than 600° F., using pressures exceeding 200 pounds per square inch (psi) under vacuum.
This type of heater is typically processed using an autoclave or Vacuum Hydraulic Press (VHP) to apply heat, pressure, and vacuum. Each of these methods has advantages and disadvantages.
Autoclave processing has the advantage that gas pressure can be used to uniformly apply hydrostatic pressure to the surfaces of the lamination stack, and that multiple lamination structures can be processed simultaneously. The disadvantages are that autoclave processing is commonly limited to a maximum pressure of 200 psi at 600° F., resulting in slow throughput rates due to equipment limitations. In addition, autoclave processing uses polymer bags and/or seals that can fail at the high processing temperatures required for lamination, resulting in leaks that cause loss of applied pressure and may cause loss of the lamination part being fabricated. Autoclave equipment is expensive and labor-intensive, as are the polymer bags and sealants used, and can be a safety hazard at the high pressures (greater than 200 psi) and high temperatures (greater than 600° F.) for lamination. Autoclaves also have long cycle times because the high thermal mass of the autoclave results in low heating rates. Likewise, pressure application rates are slow due to the high gas volumes required, which may be greater than 10 minutes to reach 200 psi.
Vacuum Hydraulic Press (VHP) processing has the advantages that high temperatures are easily achieved (greater than 1000° F.), as are high pressures (greater than 3000 psi). VHP provides rapid pressure application and high heating rates. VHP does not require expendable polymer sealants. Multiple platens and low thermal mass allow faster cycle times and multiple part throughput. In addition, VHP has a smaller “footprint” than an autoclave, and substantially lower operating costs. Thus, VHP permits overall part flow that is several times faster than with autoclave processing. However, VHP has disadvantages in that non-uniform pressure application can result when processing thin films due to compression tooling mismatch. Also, a fluid thermoplastic layer such as PFA (perfluoroalkoxy film) is required to distribute pressure. In addition, tool/platen distortion resulting from non-uniform loading within the tool can contribute to problems with lamination quality.